Question

What is the oxidation number of $Si$ in the compound $CaSi{O_3}$ ?
(A) $- 4$
(B) $+ 2$
(C) $- 2$
(D) $+ 4$

Answer 1

In simple terms, oxidation number can be defined as the number that is allocated to elements in a chemical combination. It is the count of electrons that atoms in a molecule can share, lose or gain while forming chemical bonds with other atoms of different elements.

Complete answer:
The oxidation number is used to determine the changes that occur in redox reactions. It is also called oxidation state. The charge that an atom appears to have on forming ionic bonds with other heteroatoms is called the oxidation number of that atom. In redox reactions, the atoms or ions either gain or lose electrons and have different oxidation states, before and after the chemical reaction. The oxidation number or the oxidation state of a given atom in a molecule is assigned by: summing up the constant state of other atoms that are bonded to it and equating the total oxidation state of a molecule to the total charge of the molecule.
Consider the compound $CaSi{O_3}$
The total charge present $= 0$
Oxidation number of oxygen $= - 2$
Oxidation number of calcium $= + 2$
Let the oxidation number of silicon be $x$
So, $( + 2) + x + 3( - 2) = 0$
$x = + 4$
The oxidation number of $Si$ in the compound $CaSi{O_3}$ is $+ 4$ .
Therefore, option D is the correct answer.

Note:
Remember that electropositive metal atoms of group $1,2$ and $3$ lose a specific number of electrons and they always have constant positive oxidation numbers. In molecules, the more electronegative atom gains electrons from a less electronegative atom and has negative oxidation states.